How often do you need to convert a measurement from the American standard system to the metric system? Why hasn’t the United States adopted the metric system? It’s seen as a hassle because manufactures have to convert packaging. Governent would need to adjust road signs and citizens would need to get rid of old measurement tools. The list for metric conversion goes on and on. However, it would make sense from a global perspective. If you need to know how to convert inches to centimeters or gallons to liters, then check out Unit Converters site.